New research has found that our efforts to reduce the amount of mercury in the atmosphere are bearing fruit, with levels down by almost 70% over the last 20 years.
For decades we have been emitting mercury – a pollutant that harms people and the environment – into the atmosphere through activities such as burning fossil fuels, incinerating waste, mining and cement production.
Regulations such as the Minamata Convention on Mercury have been introduced to reduce these emissions but quantifying the success of such measures is complicated. While the obvious way to check the efficacy of our efforts would be to measure the amount of mercury in the air, some of what we will be measuring will be older (legacy) mercury stored in soil and water which can be released back into the air over time.
To differentiate between newly released mercury and legacy mercury from soil, scientists analysed mercury isotopes in the atmosphere. Since long-term atmospheric data is limited, researchers from the American Chemical Society sought alternative ways to study past mercury levels.
They focused on Androsace tapete, a small perennial plant that grows in high-altitude regions on Mount Everest. Similar to tree rings, this plant produces a new layer of leaves each year, which captures the surrounding environmental conditions, including mercury levels. By analysing the inner, older leaves of two plants, the team reconstructed atmospheric mercury trends dating back to 1982.
They found that mercury in the air increased from the 1980s to 2002, reaching a peak of about 3.3 ng m³ (nanograms per cubic metre). After that, levels dropped by around 70%, reaching about 0.9 ng m³ in 2020. This drop matches patterns seen in other parts of the Northern Hemisphere, especially in rural areas of China.
In recent years, scientists also noticed a shift in the type of mercury in the air, with lighter mercury isotopes becoming more common. This suggests that the decrease in mercury is mostly due to a drop in emissions from human activity. However, mercury re-released from soil stayed fairly constant and now makes up a larger share of total emissions—from 44% in 2010 to 62% in 2020.
Yindong Tong, the corresponding author on the study, said: ‘By tracking mercury pollution over four decades at the top of the world, we show that global efforts to reduce pollution are working — mercury levels in the air around Mount Everest have dropped significantly in the last two decades.’
The research concludes on a note of caution, pointing out that to continue progress, future strategies must also address mercury being re-emitted from soil, particularly as climate change can accelerate this process in a number of ways.
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